1. A user subscribes to a a campaign via opt-in module
The campaign has a PDF attachment.

2. The user gets the email + PDF attachment

3. User deletes the message

4. After some time he wants to get the message + PDF again - so he subscribes again via the same opt-in module.
AND NOTHING - since he is already registered in the list I could not find a way to receive the message + PDF again to the same user's email address.

I tried to delete the user from the list and subscribe again - nothing happened.

I am looking for a way to enable resubmitting the messages + attachments after subscribing again even if the user is already in the list.
This is what my customer wants and the "customer is always right".

Unfortunately the logic for the module does not handle this. The catch up feature is designed to allow someone to retrospectively be added to a campaign. Not to be added, sent, delete, removed, re-added and resent.

In this rate circumstance, I think the user would need to contact the admin of the site and ask for a copy. Either that, or check their deleted folder.